1. Field of the Invention
The present invention relates generally to tubular prostheses, such as grafts, stents, stent-grafts, and the like. More particularly, the present invention provides radially expandable tubular prosthetic structures which are deployable within tortuous body lumens, particularly within branching blood vessels for the treatment of abdominal and other aneurysms.
Vascular aneurysms are the result of abnormal dilation of a blood vessel, usually resulting from disease and/or genetic predisposition, which can weaken the arterial wall and allow it to expand. While aneurysms can occur in any blood vessel, most occur in the aorta and peripheral arteries, with the majority of aortic aneurysms occurring in the abdominal aorta, usually beginning below the renal arteries and often extending into one or both of the iliac arteries.
Aortic aneurysms are most commonly treated in open surgical procedures, where the diseased vessel segment is bypassed and repaired with an artificial vascular graft. While considered to be an effective surgical technique, particularly considering the alternative of a usually fatal ruptured abdominal aortic aneurysm, conventional vascular graft surgery suffers from a number of disadvantages. The surgical procedure is complex and requires experienced surgeons and well equipped surgical facilities. Even with the best surgeons and equipment, however, patients being treated frequently are elderly and weakened from cardiovascular and other diseases, reducing the number of eligible patients. Even for eligible patients prior to rupture, conventional aneurysm repair has a relatively high mortality rate, usually from 2% to 10%. Morbidity related to the conventional surgery includes myocardial infarction, renal failure, impotence, paralysis, and other conditions. Additionally, even with successful surgery, recovery takes several weeks, and often requires a lengthy hospital stay.
In order to overcome some or all of these drawbacks, endovascular prosthesis placement for the treatment of aneurysms has been proposed. Although very promising, many of the proposed methods and apparatus suffer from undesirable limitations. In particular, proper matching of an endovascular prosthesis with the complex and highly variable vascular geometry can be problematic.
Proper matching of the prosthesis to the proximal neck of the aortic vessel and the branching blood vessels is critical to the treatment of an aneurysm. The prosthesis preferably extends axially beyond the weakened portion of the blood vessel to anchor securely in the less diseased vessel wall. To prevent the leakage of blood through a ruptured aneurysm, and also to prevent the release of thrombus from within the distended aneurysm and into the bloodstream, it is also preferable that the prosthetic lumen be substantially sealed against the healthy endothelium. The prosthetic lumen should remain open despite physiological movement of the vasculature and environmental stresses, so as to promote the free flow of blood. Furthermore, the geometry of the prosthetic lumen at the luminal intersection where the abdominal aorta meets the iliac arteries is of particular importance, as this bifurcation can have a significant impact on the relative blood flows through the two iliac arteries.
Unfortunately, the size, extent, and specific geometry of abdominal aortic aneurysms can vary widely from patient to patient. While the aneurysm is often downstream of the renal arteries, as noted above, it may begin in very close proximity to these lateral branching blood vessels, and in some cases will extend up to, above, and along the renals themselves. Additionally, while the aneurysm itself is typically a distension of the vessel wall, the path the prosthesis must follow within the diseased vessel may be fairly convoluted. For example, the abdominal aorta typically defines a significant bend between the renal arteries and the iliac arch when viewed from a lateral position. This aortic bend often remains quite pronounced despite the presence of the distended aneurysm, and complicates the sealing and anchoring of the endoluminal prosthesis adjacent the renal arteries.
Abdominal aortic aneurysms also appear to have a significant effect on the geometry of the intersection between the abdominal aorta and iliac arteries. Even among healthy patients, there are significant variations in the angles defined by the iliac arteries relative to the aorta, typically being anywhere in the range between 15-45.degree.. The variation in aorta iliac angularity is often much wider in patients seeking therapy for aneurysms. In fact, iliac arteries which branch off from an aorta with a local angle of over 90.degree. have been found in aneurysm patients.
Known branching endoluminal prostheses are generally formed as tubular, radially expandable stent-grafts. In contrast with the convoluted branchings of diseased body lumens, these stent-graft structures have typically been formed with simplistic cylindrical frames or "stents." A separate liner or "graft" is typically attached to the frame to prevent blood flow through a ruptured vessel wall. Such liners are often formed from inelastic fabrics to prevent pressure from distending a weakened luminal wall. Typically, these branching structures are primarily supported from immediately below the renal arteries. Patients may not be eligible for these known endovascular aneurysm therapies if this portion of the aorta is weakened by disease.
The branching stent-graft structures of the prior art have generally comprised uniform structures, in which the smaller iliac branch portions form cylinders which are substantially parallel to the aortic portion when the prosthesis is at rest. Although these straight branching prostheses are intended to deform somewhat to accommodate the branch angles of body lumen systems, the imposition of substantial axial bends on known endovascular stent-grafts tends to cause folding, kinking, or wrinkling which occludes their lumens and degrades their therapeutic value. Still another disadvantage of known bifurcated stent-grafts is that even when they are flexed to accommodate varying branch geometry, the prosthetic bifurcation becomes distorted, creating an unbalanced flow to the branches. To overcome these limitations, it has often been necessary to limit these highly advantageous, minimally invasive endovascular therapies to patients having vascular geometries and abdominal aortic aneurysms which fall within very narrow guidelines.
For these reasons, it would be desirable to provide improved endoluminal prostheses and methods for their use. It would further be desirable to provide improved branching endoluminal prostheses, and improved methods for placement of such prostheses. It would be particularly desirable to provide endoluminal prostheses (and methods for deploying them) which would accommodate widely varying lumen system geometries, and which would thereby increase the proportion of patients eligible to receive these highly advantageous endoluminal prosthetic therapies for treatment of abdominal aortic aneurysms and other disease conditions of the body lumen systems.
2. Description of the Background Art
U.S. patent application Ser. No. 08/538,706, filed Oct. 3, 1995, now U.S. Pat. No. 5,824,037 the full disclosure of which is hereby incorporated by reference, describes modular prostheses and construction methods. Parent Provisional Application Ser. No. 60/008,254, previously incorporated herein by reference, describes bifurcated modular prosthetic structures and methods for assembling them in situ.
U.S. Pat. No. 5,064,435 describes a self-expanding prosthesis which maintains a stable axial length during radial expansion by anchoring of radial outward flares at each end, and by sliding of an overlapping medial region therebetween. U.S. Pat. No. 5,211,658 describes a method and device for endovascular repair of an aneurysm which makes use of separately introduced frame and liner structures. A similar method of repairing blood vessels is described in U.S. Pat. No. 5,078,726, in which a locking stent is expanded within a vascular graft which has been positioned within the blood vessel. The in situ deployment of an aortic intraluminal prosthesis by a catheter having two inflatable balloons is described in U.S. Pat. No. 5,219,355.
European patent application publication no. 0 551 179 describes a method for deploying two tubular grafts which extend in parallel from the renals and into the aorta. U.S. Pat. No. 5,360,443 describes a bifurcated aortic graft which is secured to the aorta by a plastically deformable frame positioned between the renal arteries and the iliacs. Soviet Patent 145-921 describes a bifurcated blood vessel prosthesis having a fastening element which extends past the renal arteries to prevent migration. U.S. Pat. No. 4,774,949 describes a catheter having a lumen adapted to access branch arteries.
U.S. Pat. Nos. 4,550,447 and 4,647,416 describe vascular PTFE grafts which include transverse ribs integral with a tube wall, and methods for their production. U.S. Pat. No. 5,443,499 describes a radially expandable tubular prostheses for intraluminal implantation within children. U.S. Pat. Nos. 5,229,045 and 5,387,621 describe porous membranes based on unstable polymer solutions which are suitable for vascular prostheses, and methods for their production.